Physical Properties of the Blr of Ngc 5548: Long Term Variability

Here we investigate the variability of physical parameters in the broad line region (BLR) of NGC 5548 using the BP method given by Popović (2003). We apply the method on the Balmer lines observed from 1996 till 2004, and found that variability seen in lines, is also present in the electron temperature. We found that the averaged electron temperature for the period was T= 22600 K, and that varies from 12 000 K (in 2002) till 34000 K (in 1998). This variation cannot be explained with an intrinsic extinction and it presents real variability in physical parameters: the electron temperature and density. We found a high correlation between the optical continuum intensity and electron temperature (r = 0.85) that supports existence of an accretion disk in the BLR of NGC 5548.